Method for molding dental restorations and related apparatus

ABSTRACT

The present invention is concerned with a process for the formation of dental restorations from glass-ceramic materials and the resulting dental restorations. In this invention, a dental restoration is prepared by placing a glass-ceramic material in a heat-pressure deformable crucible. Heat is then applied to the crucible in order to bring the glass-ceramic material to a working range at temperatures above its liquidus temperature. The crucible in which the glass-ceramic material is placed has heat-pressure deformation properties which are matched to the working temperature of the glass-ceramic material being heated. The heat deformation properties of the crucible must be such that when the glass-ceramic material in the crucible is in the working range the crucible is heat-pressure deformable without rupturing. Once the glass-ceramic material is heated to its working temperature, the crucible is brought into contact with a mold having a preformed cavity therein, the cavity being in the shape of the desired dental restoration. As the distance between the heated glass-ceramic material and the mold is decreased, the crucible is deformed to form a seal with the mold thereby facilitating the injection of the molten glass-ceramic material into the mold cavity. An interactive seal between the crucible and the mold may be provided for. The composite process may be carried out in a vacuum. The resulting dental restoration has superior optical esthetic and strength properties. The invention further includes the heat-pressure deformable crucible.

RELATED APPLICATIONS

This application is a continuation in part application of applicationSer. No. 08/250,926 filed May 31, 1994, now U.S. Pat. No. 5,507,981issued Apr. 16, 1996.

FIELD OF THE INVENTION

The present invention relates to a process for the molding of metal freedental restorations such as crowns, bridges, inlays, onlays etc. fromglass-ceramic materials. The invention is also concerned with apparatuswhich permits dental restorations to be easily molded from glass-ceramicmaterials and lastly, the invention relates to the resulting dentalrestorations.

BACKGROUND OF THE INVENTION

In the prior art various methods have been used to form metal freedental restorations from glass-ceramic materials. Glass-ceramicmaterials because of their strength, translucency, non-toxicity andother physical properties are ideal materials for use in forming dentalrestorations. Because of their suitability, glass-ceramic materials havebeen used to form dental restorations for at least eighty years. In theprior art the most widely used means for forming dental restorationsfrom mixtures of glass and ceramic materials is a process which utilizesa slurry of glass and ceramic particles. In this process a die is formedwhich is an exact replica of the remaining portion of the tooth to whichthe restoration is to be secured. It is understood by one skilled in theart that the remaining portion of the tooth has been prepared by thedentist in such a manner that the attachment of the restoration isfacilitated. To start the process the dentist takes an impression of theprepared tooth to create a negative impression of the prepared tooth orteeth. This negative impression is then packed with a material to form apositive impression of the prepared tooth or teeth. This positiveimpression is called a die. Platinum foil is then pressed over the dieto from a matrix which is essentially a foundation on which the dentalrestoration is built. In order to form up the dental restoration manylayers of a slurry of a particulate glass-ceramic material are appliedto the platinum foil matrix. As multiple layers of the slurry are builtup and dried a semi-solid structure is formed which can be carved intothe shape of the desired dental restoration. Once the desired shape isachieved the structure is then removed from the die. At this stage thestructure is referred to as a green structure. The structure is thenfired, during the firing process the particulate glass-ceramic materialfuses into a solid mass. Because the green structure is formed frommultiple layers of the dried glass-ceramic material uneven fusing mayresult. As a result of this uneven fusing the physical properties of thefinished restoration may be detrimentally affected. As a result aninferior dental restoration results. Further, as can be seen from theabove description, the overall process is very labor intensive.

Other methods for forming the green restoration have been considered inthe prior art, for example, in U.S. Pat. No. 2,196,258, a mixture ofparticulate glass and ceramic materials which incorporates a binder ispacked into a flexible mold to form a green structure which is thenfired to form a finished structure. Again, because the process entailsthe fusing of particulate material, uneven fusing may result and hence aweakened and inferior dental restoration may result.

To overcome the problems as described above the trade has recognizedthat in order to produce strong, translucent metal free dentalrestorations it would be desirable to form these restorations directlyfrom a homogenous molten glass-ceramic material. It was realized that itmay be possible to produce a satisfactory restoration by forcing amolten or plastic glass-ceramic material into a mold having a cavity inthe form of the desired dental restoration. The prior art furtherrecognized that the glass-ceramic material could be introduced into thecavity when the glass-ceramic material was in the liquid or in theplastic state.

A constant goal of the prior art as described, was to effect the moldingprocess in a quick and efficient manner and in a manner that produces adental restoration that has excellent definition and fit. In dentalrestorations definition is extremely important, as in order to have asatisfactory restoration the finest details of the original tooth mustbe reproduced. For example, for a dental restoration to be successfulthe margins must be sharp and well defined. It is in this area that theprior art molding processes are deficient in that it was not possible toachieve the desired degree of definition.

Further, it is desirable to produce a dental restoration in a shortperiod of time in order to efficiently utilize the overhead of thedental laboratory and in order to minimize the labor content of thedental restoration.

Dental laboratories are not typically well funded operations. Therefore,in order to keep cost to a minimum it is highly desirable that asuitable process for forming dental restorations utilize equipment whichis relatively inexpensive. While the above described process fits thisrequirement the below described DICOR process does not.

As is discussed above, there are several prior art processes for themanufacture of dental restorations from glass-ceramic materials. Arecent addition to the prior art is the DICOR process as sold by theDentsply International, Inc. of York Pa. In this process a dentalrestoration is formed by centrifugal casting of a molten glass-ceramicmaterial. This process is further described in U.S. Pat. No. 4,431,420issued Feb. 14, 1984 and related patents. Centrifugal casting has beenextensively used in the casting of metals principally by the lost waxprocess. Further, this process has been imminently successful forhundreds of years for use in conjunction with metals. This successresults from the fact that molten metals have very low viscosity andhigh density in the molten state, hence, they function very well incentrifugal casting processes. That is, because molten metals have ahigh density and a very low viscosity in the molten state centrifugalforce is adequate for purposes of injecting the molten metal into apreformed mold cavity. In an attempt to produce dental restorationswhich have high definition the above mentioned DICOR process usescentrifugal force to form the desired dental restorations from a moltenglass-ceramic material. Molten glass-ceramic materials have a muchhigher viscosity and a much lower density when compared to moltenmetals. For this reason, it is not possible to consistently drive amolten glass-ceramic material, by centrifugal force alone into a mold inorder to produce a satisfactory dental restoration. That is, a moltenglass-ceramic material cannot be driven by centrifugal force into a moldcavity with sufficient force in order to always get the requireddefinition, necessary to form a satisfactory dental restoration. It iswell recognized by one skilled in the art that in order to have asatisfactory dental restoration, excellent definition must be achievedin order to recreate the desired margins which are needed for the properfit of a dental restoration into the human mouth.

Further, the DICOR process, is deficient as to the coloration of theglass-ceramic material utilized. The resulting Dicor dental restorationhad an undesirable white color and must be glazed in order to producesatisfactory human coloration. As a result the coloration is only on thesurface of the dental restoration, If adjustment by grinding is neededin the final installation of the restoration into the human mouth theglazing is removed thereby exposing the whitish base which contrastswith the glaze. This contrast is very unsatisfactory from an estheticpoint of view.

In contrast to this deficiency, the restoration of the subject processis adapted to utilize glass-ceramic materials wherein the coloration ofthe resulting dental restoration, throughout, approximates human toothcoloration. Hence, if grinding is necessary in final fitting contrastbetween the surface of the dental restoration and the underlying base isnot observed.

Undesirable contrast can also result from normal wear, where as a resultof the grinding action of one tooth against another the glaze is wornaway. Again, this is not a problem in this invention as the preferredglass-ceramic material has a uniform natural coloration throughout. Itshould be noted that the restoration of the subject invention may beglazed to achieve the exact shade desired.

In contrast to the above discussed prior art processes, the process ofthe subject invention utilizes a positive mechanically applied force forpurposes of injecting the molten dental glass-ceramic material into thepreformed mold cavity.

For a dental glass-ceramic material to be satisfactory for use in theformation of dental restorations the material should incorporate many orall of the following properties:

1. It must be inert and non-toxic in an oral environment.

2. It must have sufficient structural integrity to resist the forces ofmastication and generally must have a 3-point MOR of at least 30,000PSI.

3. Should be capable of being formed into forms which are compatiblewith the human anatomy using simple equipment.

4. Should have esthetic qualities (coloration similar to human teethwith a slightly translucent appearance) which are compatible with humanteeth and hence should be monolithic or glazable.

5. Further, the glass-ceramic material must not absorb moisture or stainand it must be stress corrosion resistant.

6. Likewise the glass-ceramic material should have wear characteristicswhich are similar to natural human teeth and should be compatible withother dental materials.

7. The glass-ceramic likewise must have dimensional stability and resistthermal shock during processing and in particular it must havedimensional stability during subsequent heat treating processes whereinrecrystalization is effected.

8. Further, the glass-ceramic material should be compatible from athermal expansion point of view with metals, stains, glazes etc. as areconventionally used to form dental restorations.

9. In order to create an esthetically pleasing dental restoration it maybe necessary to alter the final dental restoration to the exact shapeand shade desired. In order to effect these alterations the dentalrestoration must be heated to a temperature of about 950° C. for eachoperation. Therefore, a satisfactory glass-ceramic material must becapable of withstanding multiple heat cycles to about 950° C.

10. A suitable glass-ceramic material must be capable of retaining itsstructural integrity during heat treating.

11. In summary a suitable glass-ceramic material should have;

A. Coefficient thermal expansions (C.T.E.) of 5 to 145×10⁻⁷ /°C.

B. Translucency of 2.5 to 4.0 on a visible scale of 0 (clear) to 5(opaque) and overall beauty.

C. M.O.R. of at least 30 K.S.I. average.

D. Ability to be heat treated to 925°-950° C.

E. Structural integrity during heat treat

F. Meltability and formability

G. Chemical durability in an oral environment

The subject invention includes glass-ceramic materials which meet theabove set forth criteria.

SUMMARY OF THE INVENTION

In accordance with the above description, it is obvious that inaccordance with the prior art it is difficult, if not impossible, toform top quality dental restorations by molding glass-ceramic materialsin an inexpensive and efficient manner.

The process, apparatus, compositions and dental restoration of thesubject invention provide improvements over the prior art. By use of theprocess of the subject invention glass-ceramic materials can be readilymolded into dental restorations. Further, the apparatus of the subjectinvention is relatively inexpensive and is easy to utilize. Thecompositions of the subject invention are highly advantageous in thatthey produce esthetically pleasing dental restorations which arechemically inert in the human mouth and have outstanding strengthproperties. Further, the compositions of this invention are advantageousin that when dental restorations formed from these compositions are heattreated they maintain their structural integrity. Further, these dentalrestorations are capable of withstanding multiple heat cycles to about950° C., possess thermal expansions which are compatable with theexisting porcelains and therefore, these dental restorations can bereadily altered using conventional porcelain materials.

Likewise, dental restorations in accordance with the present inventionhave acceptable coloration after heat treating and can be used at thatstage, without further cosmetic treatment, in the mouth. In order toenhance the esthetic properties of the resulting dental restoration, thedental restoration can be readily altered using porcelain materials toachieve any desired effect.

Accordingly, it is an object of the present invention to provide anefficient process whereby dental restorations may be molded fromglass-ceramic materials.

It is a further object of the present invention to provide an apparatusfor the molding of glass-ceramic dental restorations which is easy touse, is lab friendly, and which is reasonably priced.

It is a further object of the present invention to provide glass-ceramicdental restorations which have outstanding strength and are estheticallypleasing.

It is also an object of this invention to provide glass-ceramiccompositions, which are suitable for the formation of dentalrestorations which have a high degree of micro-structural control duringthe development of the crystals thereby permitting great flexibility inthe forming of these dental restorations.

It is still another object of the present invention to provide aglass-ceramic material which will maintain its structural integrityduring heat treating and, in particular, will not slump or sag duringheat treating outside of the investment.

Another object of the present inventions is a glass-ceramic materialwhich is suitable for the formation of dental restorations and which iscapable of maintaining its translucency during multiple firing cycles toapproximately 950° C.

Still another object of this invention is a process for forming aceramic dental restoration.

Wherein the process comprises:

A. placing a glass-ceramic material in a heat-pressure deformablecrucible;

B. heating the crucible and glass-ceramic material to a temperature atwhich said crucible becomes heat-pressure deformable and theglass-ceramic material is moldable;

C. bringing the heated crucible into contact with a mold having apreformed cavity therein;

D. continuing to move the crucible into contact with the mold therebycausing the crucible to deform against the mold, and causing themoldable glass-ceramic material to be injected into said cavity, therebyforming a dental restoration;

E. cooling the mold and the ceramic dental restoration therein;

F. removing the formed ceramic restoration from the mold;

G. heat treating the dental restoration; and

H. finishing the dental restoration.

Also an object of this invention is to form a heat deformable cruciblehaving a base and a side portion wherein said crucible is formed by theheat sintering of a particulate mixture of glass and a metal oxide. Apreferred composition comprises from about 27 to percent glass and fromabout 69 to about 73 percent of a metal oxide.

Another object of this invention is a dental restoration which is formedfrom a glass ceramic material having the following composition (byweight percent);

    ______________________________________                                        Li.sub.2 O        8-15                                                        Al.sub.2 O.sub.3 1.5-5.0                                                      SiO.sub.2        60-85                                                        Na.sub.2 O       0-2                                                          K.sub.2 O        0-2                                                          P.sub.2 O.sub.5  1.5-5                                                        ZrO.sub.2        0-3                                                          CaO              0-1                                                          BaO + SrO + LaO   0-12                                                        Coloring oxide   0-5                                                          ______________________________________                                    

Lastly, an object of the present invention is to create a glass-ceramicmaterial which has excellent chemical durability and as such will notdeteriorate when exposed to the fluids in the human mouth.

These and other objects, features and advantageous of the presentinvention will become apparent from the detailed description herein.

The advantages of the present invention can be more clearly understoodfrom the following description taken together with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart showing the steps of the preferred embodiment ofthe process of this invention.

FIG. 2 shows a sectioned lost wax mold for use in the invention.

FIG. 3 shows a sectioned structure illustrating the heating step of thisinvention.

FIG. 4 shows a sectioned structure illustrating the initial contact ofthe crucible with the mold.

FIG. 5 shows a sectioned structure illustrating the partial sealing ofthe crucible against the mold.

FIG. 6 shows a sectioned structure illustrating the complete sealing ofthe crucible against the mold and the injection of the moltenglass-ceramic into the mold cavity.

FIG. 7 is a sectioned side view showing the composite apparatus of thisinvention.

FIG. 7a and 7b are sectional side views showing the preferred compositeapparatus of this invention.

FIG. 8 shows a sectioned alternate mold.

FIG. 9 shows a sectioned alternate mold.

FIG. 10 shows the mold of FIG. 9 being filled with a moltenglass-ceramic.

It should be noted that FIGS. 2 to 10 are schematic representations ofapparatus which may be useful in this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 generally describes the overall process of the subject inventionwherein dental restorations are formed by the molding of a glass-ceramicmaterial. As can be seen in FIG. 1, the first step is the formation of amold having a suitable mold cavity therein. To start the process wherebythe mold cavity is formed the tooth or teeth in the human mouth areprepared by the dentist by procedures which are commonly known in theprior art. By using impressions which are provided by the dentist apositive wax form is produced of the desired dental restoration. Thispositive wax form is then positioned in a mold usually called a ring. Asemi-liquid investment material is then poured around the positive waxform. Once the investment material sets up and cures the resulting moldis placed in a furnace and heated thereby causing the wax to melt andrun out of a sprue hole which is integral with the mold. The finishedmold is then complete. This constitutes the formation of a mold by thelost wax process.

In the second step of FIG. 1 a button of a glass-ceramic material isplaced in deformable crucible 8, as is illustrated in FIG. 3. The buttonof glass-ceramic material constitutes a small cylinder of theglass-ceramic material which usually weighs about six grams and has adiameter of about two cm. and a thickness of about one cm. These buttonsof glass-ceramic materials are a convenient shape whereby thesematerials may be manufactured, sold and used. It is understood by oneskilled in the art that a sufficient amount of the glass-ceramicmaterial must be used in order to form the desired dental restoration.

In the third step of FIG. 1 crucible 8 and the button of glass-ceramicmaterial 7 is uniformly heated. The glass-ceramic material is heated toa temperature above its liquidus temperature as will be described ingreater detail herein below. Further the heat-pressure deformablecrucible 8 will be described in greater detail herein below.

In the process of this invention the preformed mold can incorporatemultiple cavities in order that more than one dental restoration can beproduced during one cycle of the subject process.

In steps four, five and six of FIG. 1 the heated crucible andglass-ceramic material are moved into contact with the mold bymechanical means in a manner which will be described in greater detailrelative to the discussion of FIGS. 3 to 6 herein below.

In accordance with steps 7 and 8 of FIG. 1 the mold is cooled and thesolidified glass-ceramic casting is removed from the investment bymechanical means. The dental restoration is then cut off the sprue andfinished by heat treating polishing and/or glazing in order to achievethe desired esthetic effect.

The process of this invention may utilize both glass and glass-ceramicmaterials for purposes of forming the desired dental restoration.

For strength and esthetic reasons, it is preferred that a glass-ceramicmaterial be utilized. When a glass-ceramic material is utilized, thebutton of glass-ceramic material 7 is initially placed in crucible 8 ina glass phase. As heat is applied to crucible 8, glass-ceramic material7 is heated. As the heating of the glass-ceramic material 7 continues,crystal formation is effected whereby glass-ceramic material 7 becomes aceramic via the formation a of crystalline phase. As the heating iscontinued, the glass matrix slowly dissolves the crystalline phasethereby causing the glass-ceramic material 7 to reenter the glass phase.The temperature at which the crystal phase completely dissolves in theglass matrix is defined as the liquidus temperature of the glass-ceramicmaterial. In accordance with this invention, it is found desirable toheat the glass-ceramic material to a temperature above the liquidustemperature in order to eliminate any possibility of the existence of acrystalline phase in the molten material. Further at this temperaturethe glass-ceramic material has a viscosity of about log 3 to about log 4P which is suitable to allow the molten glass-ceramic material to bereadily injected into the mold cavity 5. The viscosity at thistemperature is defined as the working range.

Throughout this application, the viscosity of the molten glass-ceramicmaterials and of the soften crucible will be defined as the log of therespective viscosity in poises. Further, the unit poise will beabbreviated as P. For example, if the viscosity of a moltenglass-ceramic glass material is 10⁴ poises the viscosity will beindicated by log 4 P.

While FIG. 1 illustrates the broad process of the subject invention. Theindividual steps as illustrated in FIG. 1 are defined in greater detailin the description of FIGS. 2 through FIG. 10.

In FIG. 2, it can be seen that mold 4 has been formed by the placementof an investment material 10 in ring 12. Prior to the placement ofinvestment material 10 in ring 12, ring 12 is positioned around wax form14, the upper extremity of which is shaped in the form of a desireddental restoration 16. Wax form 14 is only shown in an outline form, asFIG. 2 illustrates a finished mold 4 after wax form 14 has been burntout.

The procedure whereby mold 4 is formed is generally known in the priorart, and has been used for centuries to form lost wax molds for use inmetal casting procedures. As is stated above in the preparation of mold4, wax form 14 is positioned in ring 12 an investment slurry 10 is thenslowly poured into ring 12 usually with the aid of vibratory techniquesto insure that investment 10 completely fills ring 12, and inparticular, completely encases wax form 14. Wax form 14 further includesan elongated sprew section 5. Again, these procedures are commonly knownin the prior art.

FIGS. 3, 4, 5, and 6 show the general process of the subject inventionin a schematic form.

Referring to FIG. 3, it can be seen that mold 4 having cavity 14 ispositioned in the vicinity of crucible 8. Positioned in crucible 8 isglass-ceramic material 7, the details of which will be described herein.Crucible 8 is further positioned on a ceramic base 21 which ispositioned on ram 22 whereby crucible 8 can be moved in relation to mold4. An electric heating element 24 is further provided whereby heat canbe applied to crucible 8. Details of the heating of glass-ceramicmaterial 7 will be discussed herein below.

During the heating of crucible 8 glass-ceramic material 7 is convertedfrom the solid state to the liquid state, and crucible 8 converted froma solid brittle state to a plastic state wherein it is heat-pressuredeformable. Once the glass-ceramic material 7 reaches the desiredworking range, ram 22 is actuated as is illustrated in FIG. 4, therebycausing crucible 8 to move upwardly and to come into contact with thelower extremities of mold 4. The actuation of ram 22 is effected by apower source not shown.

As can be seen in FIG. 5 as the upward movement of ram 22 continues,crucible 8 continues to deform against mold 4 causing the upperextremities of crucible 8 to seal against mold 4 at interface 28.Further, it can be seen that molten glass-ceramic material 7 has startedto flow into mold cavity 14.

Referring to FIG. 6, as the travel of ram 22 continues the deformationof crucible 8 against mold 4 is completed, and further cavity 14 iscompletely filled with glass-ceramic material 7 as a result of theapplied pressure of ram 22.

Subsequent to the procedures as are illustrated in FIGS. 3 through 6,mold 4 is then cooled and the desired dental restoration is removed frominvestment 10. Once the dental restoration is removed from investment10, the dental restoration is cut apart from the sprue and is heattreated and finished by polishing and glazing in order to achieve thedesired esthetic effect.

Further, after formation dental restoration 26 is heat treated in such amanner that its strength and other properties are enhanced by theformation of crystals in a glass matrix. The details of heat treatingare described below.

FIG. 7 illustrates apparatus 32 which may be utilized to effect thecomposite process which is illustrated in the flow chart of FIG. 1. Thisapparatus generally comprises support frame 30, heat source 33, moldretaining means 34 and a plunger 36. Support frame 30 generallycomprises the outside frame of apparatus 32.

Mold retaining means 34 comprises a bar 50 into which is threaded moldclamp 35. As can be seen, bar 50 permits mold 4 to be locked to supportbar 44. Support bar 44 further incorporates an aperture 56 which isslightly smaller than the diameter of mold 4 and slightly larger thanthe diameter of crucible 8. By the actuation of ram 36, crucible 8 ismoved up into contact with mold 4 in a manner which is similar to thatas is described above in conjunction with FIGS. 4, 5 and 6. Theapparatus of FIG. 7 further incorporates a heat source 37, which ispreferably an electric heating element, which in the illustratedembodiment comprises an electric resistance heating element 37. In thepreferred embodiment the heating element is molybdium disilicide. Heatsource 37, which is preferably an electric heating element, iscontrolled by a power control source 58.

As is illustrated in FIGS. 3 and 7, an electric resistance heater may beutilized to effect the heating of crucible 8 and, hence, glass-ceramicmaterial 7. In addition to the electric resistance heating, asillustrated heating may be effected via induction heating, gas torchheating, or any other appropriate means.

The apparatus further may incorporate rotating means, not shown, wherebyram 36 may be rotated during the heating process in order to effect amore uniform heating of crucible 8 and glass-ceramic material containedtherein. The rotating means may be an electric, pneumatic or hydraulicmotor. Ram 36 is further provided with means for effecting its upwardmovement, which in the preferred embodiment is a pneumatic cylinder 39.

Further, referring to FIG. 7, it can be seen that apparatus 32incorporates a plurality of structural insulating members 41, 43, 45, 47and 49 which support and contain heating element 37, and contain theheat created during the operation of the element 37. These structuralinsulating members are formed from ceramic fiber board.

Likewise, it can be seen that support bar 44 incorporates an aperture 56which has a waist section 55. Waist section 55 is advantageous in thatwhen crucible 8 deforms against mold 4 the deforming upper extremitiesof crucible 8 are prevented from downward movement at the constrictionof waist 55 thereby causing the molten glass-ceramic material to beefficiently injected into the preformed cavity 14 in mold 4. That is,because upper extremities of crucible 8 are caused to solidify in thevicinity of waist 55, the downward movement of the molten glass-ceramicmaterial is prevented, thereby causing the glass-ceramic material to beinjected into mold cavity 14.

FIG. 7a and 7b represent the preferred apparatus 31 for use inaccordance with this invention. Most of the components of the preferredapparatus 31 are identical or similar to the components of apparatus 32as discussed herein above. Apparatus 31 differs from apparatus 32primarily in that a movable arm 38 is provided for wherein a preheatedmold 4 may be brought into position for the molding process andpositioned against furnace base 41. Moveable arm 38 may be connected toa central pivot point whereby it may be swung into position or it can belaterally moved into position.

Prior to moving arm 38 into position, as is shown in FIG. 7 a ram 22 isextended in order to place crucible 8 in heat source 33, wherebyglass-ceramic material 7 may be melted. Once this melting is effectedram 22 is withdrawn and moveable arm 38 is swung into place to theposition as is illustrated in FIG. 7b. In this position the formingsequence as is shown in FIGS. 2 to 6 can be completed.

Relative to apparatus 31 and 32 it is understood by one skilled in theart that crucible 8 may be placed in position on ceramic base 21 eithermanually or by automatic means.

The above described FIGS. 1 to 7b illustrate the formation of a dentalrestoration. In addition to being useful in the formation of essentiallycomplete dental restorations, the composition and process of the subjectinvention may be used to form copings over which porcelain materials maybe applied to alter and shade the dental restoration.

In the prior art, metal copings are extensively utilized. These copingsare covered with layers of porcelain materials which are applied to themetal copings for purposes of forming a composite dental restorationwhich comprises a metal base and a porcelain exterior portion. Compositestructures are advantageous in that a metal coping significantelyenhances the strength of the resulting dental restoration. Metal copingsare disadvantagous in that they are opaque and they have a color whichcontrasts with the color of a natural tooth and, further, they havetoxicity problems in some instances. The use of the subject invention toform an all glass-ceramic dental restoration is advantagous in that thecoping is essentially the same color as a natural tooth and, inparticular, it is essentailly the same color as the porcelain from whichthe exterior portion of the dental restoration is formed. Further, theall ceramic structure is advantagous in that problems resulting forcertain patients who are allergic to certain metals are eliminated. Inthis procedure, metal free crowns and bridges of outstanding strengthand esthetic properties are achieved. The outstanding estheticproperties results from the fact that these glass-ceramic copings can beutilized as a base over which a variety of different porcelains can befired in order to achieve the most delicate coloration and estheticproperties.

As is stated above, the process of the invention may utilize both glassand glass-ceramic materials. Preferred glass-ceramic compositions foruse in accordance with the invention are listed in Tables I to IV. Allcomponents listed in Tables I to IV are in weight percent.

The subject invention can utilize any suitable glass-ceramic materialsAs is shown in Table I to IV preferred glass-ceramic materials for usein this invention are lithium disilicate glass-ceramic materials. Inthese materials Li₂ O 2(SiO₂) constitutes the crystalline phase, of theheat treated glass ceramic material. Lithium disilicate glass-ceramicmaterials are particularly suited for use in the invention in that theyare non-toxic, they resist thermal shock, have excellent strength, arecorrosion resistant and they produce dental restorations whichapproximate humane coloration and are translucent and estheticallypleasing. Further, lithium disilicate glass-ceramic materials areadvantageous in that they maintain their structural integrity duringheat treating, in that they do not slump or sag during proper heattreating.

Other lithium disilicate glass-ceramic materials which may be used inthis invention are disclosed in U.S. Pat. No. 5,219,799 issued Jun. 15,1993.

Lithium disilicate glass-ceramic materials may utilize P₂ O₅ as anucleating agent. Other nuculating agents are TiO₂ and ZrO₂.

Glass-ceramic compositions which may be useful in this invention are asper Table I. The percentages of Table I and the other tables herein arein weight per cent.

                  TABLE I                                                         ______________________________________                                        Li.sub.2 O        8-15                                                        Al.sub.2 O.sub.3 1.5-5.0                                                      SiO.sub.2        60-85                                                        Na.sub.2 O       0-2                                                          K.sub.2 O        0-2                                                          P.sub.2 O.sub.5  1.5-5                                                        ZrO.sub.2        0-3                                                          CaO              0-1                                                          BaO + SrO + LaO   0-12                                                        Coloring Oxides  0-5                                                          ______________________________________                                    

More specific glass-ceramic compositions which may be useful in theinvention are as per Table II. In particular the compositions of TableII are useful in conjunction with either high or low fusing porcelainswhich may be used to alter, shade or glaze the dental restorations ofthis invention.

                  TABLE II                                                        ______________________________________                                        Li.sub.2 O         10-13.5                                                    Al.sub.2 O.sub.2 2-3                                                          SiO.sub.2        70-84                                                        K.sub.2 O        0-1                                                          P.sub.2 O.sub.5  1.5-4                                                        ZrO.sub.2        0-1                                                          BaO + SrO + LaO  .5-4                                                         CaO              0-1                                                          Coloring Oxides  0-5                                                          ______________________________________                                    

In some instances it is desirable to form a dental restoration which canbe altered, or glazed with a low fusing porcelain. For purposes of thisapplication a low fusing porcelain is defined as a porcelain which fusesat a temperature of about 700° C.

Specific glass-ceramic compositions which are useful in conjunction withlow fusing porcelains are as per Table III.

                  TABLE III                                                       ______________________________________                                        Li.sub.2 O       9-13                                                         Al.sub.2 O.sub.3 1.5-4                                                        SiO.sub.2        65-84                                                        Na.sub.2 O       0-1                                                          K.sub.2 O        0-1                                                          P.sub.2 O.sub.5  1.5-4                                                        ZrO.sub.2        0-1                                                          BaO + SrO + LaO   0-12                                                        CaO              0-1                                                          Coloring Oxides  0-5                                                          ______________________________________                                    

Specific glass-ceramic compositions which may be useful in thisinvention are as per Table IV.

                                      TABLE IV                                    __________________________________________________________________________    1     2  3  4  5  6  7  8  9  10 11 12 13 14 15 16 17 18 19 20                __________________________________________________________________________    SiO.sub.2                                                                        81.0                                                                             84.0                                                                             84.0                                                                             83.0                                                                             82.0                                                                             84.0                                                                             81.0                                                                             83.0                                                                             83.0                                                                             81.5                                                                             80.0                                                                             86.0                                                                             84.0                                                                             81.0                                                                             82.0                                                                             82.0                                                                             81.0                                                                             78.5                                                                             80.6                                                                             72.5              Al.sub.2 O.sub.3                                                                 3.5                                                                              3.0                                                                              3.0                                                                              3.0                                                                              4.0                                                                              3.3                                                                              3.3                                                                              3.5                                                                              3.5                                                                              3.0                                                                              6.0                                                                              1.5   3.0                                                                              3.3                                                                              3.5                                                                              3.0                                                                              2.5    2.3                                                                    2.5                     Li.sub.2 O                                                                       11.0                                                                             10.5                                                                             10.5                                                                             10.5                                                                             10.5                                                                             10.0                                                                             11.0                                                                             9.0                                                                              8.0                                                                              12.0                                                                             10.5                                                                             10.5                                                                             11.0                                                                             11.0                                                                             10.0                                                                             10.0                                                                             11.0                                                                             10.5   12.5                                                                   10.5                    P.sub.2 O.sub.3                                                                  3.0                                                                              2.0                                                                              2.0                                                                              2.0                                                                              2.0                                                                              1.5                                                                              1.5                                                                              3.0                                                                              3.0                                                                              2.0                                                                              2.0                                                                              2.0                                                                              3.0                                                                              1.0                                                                              1.5                                                                              2.2                                                                              3.0                                                                              2.0    2.0                                                                    2.0                     ZrO.sub.2                                                                        1.0                                                                              0.5   0.5                                                                              0.5   2.0      0.5                                                                              0.5   1.0                                                                              2.0   2.0                                                                              1.0                                                                              0.5    1.0                                                                    0.5                     TiO.sub.2                                                                        0.4            0.1                                                                              1.0                                                                              0.5            0.4                                                                              0.4   0.5                                                                              0.4                                                                              0.1    0.1                                                                    0.1                     CaO                                                                              0.5                                                                              0.25                                                                             0.25                                                                             0.25                                                                             0.25                                                                             0.25                                                                             0.25                                                                             0.25                                                                             0.25                                                                             0.25                                                                             0.25  0.50                                                                             0.50  0.25                                                                             0.50                                                                             0.35   0.35                                                                   0.42                    MnO.sub.2                                                                           0.5                                                                              0.5                                                                              0.5                                                                              0.5         0.5                                                                              0.5                                                                              0.5                                                                              0.5                      0.75             NiO.sub.2            0.06                             0.02   0.02             K.sub.2 O                                                                              0.5                                                                              0.5                                                                              0.5                                                                              1.0      1.0                                                                              0.5                                                                              0.5                  0.5    0.5              Na.sub.2 O                                                                       0.5            0.2                                                                              0.2                                                                              0.5                                                                              0.5               0.2                                                                              3.0                           Fe.sub.2 O.sub.3  0.09                                                                             0.09                                                                             0.09                    0.09                          BaO                                          3.0      3.0    0.5                                                                    9.0                     MgO                     1.0                                                   CaO                        1.0                        0.4    0.4                                                                    0.4                     __________________________________________________________________________

As to a general range of compositions which are preferred for use inconjunction with this invention the glass-ceramic compositions asdefined in Table II are preferred.

The most preferred glass-ceramic composition for use in accordance withthis invention is the glass-ceramic composition as is defined bycomposition 18 of Table IV.

The glass-ceramic composition as defined by Table I to IV above areparticularly advantageous over the prior art in that;

1. They are stronger than the prior art glass-ceramic compositions.

2. Those compositions which incorporate barium and cerium oxides areflorescent in ultra violet light.

3. The expansion rates of many of these glass ceramic compositions arecompatable with the expansion rate of existing altering porcelainmaterials.

4. They retain their structural integrity at higher temperatures thanthose of the prior art, thereby permitting altering at highertemperatures.

As is listed in Tables I to IV, coloring oxides may be added to theglass-ceramic material in order to achieve the desired coloration of theglass-ceramic dental restoration.

Suitable coloring oxides for use in glass-ceramic compositions which canbe used in this invention, some of which are illustrated in Table I toIV are SnO₂, MnO, CeO, Fe₂ O₃, Ni₂ O, V₂ O₃, Cr₂ O₃, TiO₂ etc. Thesecoloring oxides may be used singularly or in combination.

After formation of a glass-ceramic restoration in accordance with theprocess of this invention, the resulting dental restoration is heattreated in order to effect the formation of crystals in the dentalrestoration. This crystal formation is generally referred to as heattreating and enhances the physical and esthetic properties of the dentalrestoration. A suitable heat treating sequence for use with theglass-ceramic compositions of Tables I to IV is as per Table V below.

For the glass compositions which may be used in this invention the bestnucleating temperatures are about 25° to 50° C. above the upper annealpoint of the glass-ceramic. It has also been determined that a slowincrease in temperature from just above the upper anneal point to some50° C. higher produces the best results in achieving maximum nucleation.It is also well known that the temperature then must be raised to ahigher temperature to affect crystallization, this temperature dependsupon the composition of the particular glass-ceramic material beingused.

If the heating sequence in the heat treating stage is improper or isincorrectly controlled the dental restoration may slump or deform. It isunderstood by one skilled in the art that an optimum heat treatingprocedure should be developed for each particular glass-ceramic materialin order to allow the dental restoration to maintain its structuralintegrity during the heat treating process.

In the preferred embodiment the heat treat cycle is such that in thecrystalline phase the glass-ceramic material incorporates a large numberof fine crystals which are evenly dispersed through out the glassmatrix. It has been found that when the crystalline phase is very fineand evenly dispersed a dental restoration of maximum strength results.Further a fine crystalline structure tends to produce translucent dentalrestorations.

From the above discussion it is obvious that dental restorationsproduced in accordance with this invention can be heat treated after thedental restoration is removed from the investment material and the sprueis cut away.

In accordance with an alternate preferred embodiment of this inventionthe heat treating of the dental restoration may be effected while thedental restoration is still in the invested state. That is heat treatingcan be effected while the dental restoration is still encased in theinvestment material.

In accordance with still another embodiment, the dental restoration canbe removed from the investment material in which it was formed andfinished or partially finished prior to heat treating. For heat treatingthe material is then reinvested in an investment material which enhancesthe heat treatment process. After reinvestment the heat treating iscarried out in accordance with the procedure described above.

Whenever the dental restoration is heat treated in the invested statethe shrinkage of the dental restoration is minimized if not eliminated.

In heat treating and in particular in the formation of a crystallinephase shrinkage of the dental restoration occurs. This shrinkage canamount to 3 percent. Naturally, this shrinkage is undesirable as itadversely affects the fit of the dental restoration back into thepatients mouth.

As a way of overcoming the shrinkage problem, it is within the scope ofthis invention to invest the wax form in an investment material whichexpands when it hardens and is heated. That is the investment materialexpands when it hardens to produce an oversize mold cavity. Thisoversize mold cavity naturally produces an oversize dental restoration.This oversize dental restoration is then shrunk back to the correct sizeduring the heat treating process.

For example since the glass-ceramic material shrinks about 3 percentduring the heat treating process the original wax form may be investedusing an investment material which expands about 3 percent when ithardens and is heated. Using this procedure a dental restoration whichis 3 percent oversize results. This oversize dental restoration is thenheat treated whereupon it shrinks about 3 percent to produce a finisheddental restoration of the correct size.

In order to achieve proper fit, if the restoration is to be heat treatedafter removal from the investment, an investment material which expandson hardening and heating by about 3 percent must be used. Investmentmaterials which are useful with metals are not particularly suited foruse in the invention as they only expand about 1.75 percent. Investmentswhich expand about 3 percent upon hardening and heating and hence permitthis type of process are manufactured by Whipmix Corporation ofLouville, Ky. and sold under the designation GIJM 3-23-94; 1

The preferred heat treating process for use with the glass-ceramiccompositions of Table I to IV is as per Table V

                  TABLE V                                                         ______________________________________                                        Heat Restoration To                                                                             500                                                         Ramp or Soak at   500-600° C. for 2-6 hours                            Ramp at           600-925° C. for 2-3 hours                            Soak at           925° C. for 1-2 hours                                Cool to           Room temperature                                            ______________________________________                                    

After heat treating the resulting dental restoration may be furtherfinished. This finishing may include a step wherein the dentalrestoration is altered with one or more porcelains in order to achievethe precise shape, shade and shading desired. For those glass-ceramicmaterials of Tables I to IV which have a C.T.E. (Coeficient of ThermalExpansion) of from about 135 to about 145 at the set point temperature,it is desired that the C.T.E. of the altering porcelain material be fromabout 125 to about 135 and always less the C.T.E. of the glass ceramicmaterial. The process wherein the C.T.E. is measured is defined in thedescription of the Examples herein below.

Deformable crucible 8 is a critical part of the subject invention.Crucible 8 in its preferred embodiment has a circular base and hence isgenerally cylindrical. However it is understood by one skilled in theart that the crucible of this invention can have configurations otherthat circular. The crucible is formed by heat sintering a particulatemixture of components, such as, fused silica, aluminum oxide, zirconiumoxide, magnesium oxide with a glass such as borosilicate glass, sodalime glass, bottle glass, window glass, etc., clay or other materialsthat those skilled in the art of crucible making might use, to form acrucible suitable for use with a glass-ceramic material. In the broadconcept of this invention one forms the crucible of a mixture ofmaterials, such that, at the temperature where the glass-ceramicmaterial is in the working range of about log 3 to log 4 P the cruciblehas a viscosity of about log 5 to log 7 P.

Crucibles for use in this invention are formed by slip casting. Theformation of crucibles by slip casting is well known to those skilled inthe art and is described in greater detail in the Examples below.

In the description, as set forth above, the compositions which are usedto form crucibles which are useful in this invention may utilize a widerange of materials. While many glasses can be used to form crucibleswhich are useful in the subject invention, because of their toxicity,glasses which contain heavy metals such as lead, cadmium etc. should notbe used.

An alternate method for the formation of crucibles for use in thisinvention is by powder pressing and then sintered.

In this invention the composition from which the crucible is formedcontains materials such that it will be heat-pressure deformable at thedesired temperature i.e. about log 3 to log 4 P working temperature ofthe glass-ceramic. The heat-pressure deformation properties of thecrucibles used in this invention is to be contrasted with the cruciblesof the prior art which are designed to be rigid at the workingtemperature of the glass-ceramic material which is contained therein.

In the alternate structure, as is shown in FIGS. 8, 9, and 10, thesealing of the deformed crucible against the mold is enhanced. In thestructure as shown, mold 64 incorporates a circular depression 66 havingvertical walls 68 and 70 to which crucible 8 may seal. Vertical walls 72and 74 of mold 65 may further incorporate a plurality of annular grooves76. As is further shown in FIG. 10, the sealing of crucible 8 againstmold 65 is enhanced by the flowing of the upper extremities of crucible8 into annular grooves 76 during the deformation process.

EXAMPLES

The present invention is illustrated by the following Examples however,these examples are not to be construed as limiting the invention.

Dental restorations were prepared in accordance with the below listedexamples. In these examples wax models of a tooth were prepared. A spruewas then attached to the wax model. The wax model with the sprueattached was then placed in an investment ring. An investment materialwas then prepared by mixing 90 gram of Kerr Thermovest with 17 ml of amixture of 2 parts of Thermovest liquid with 1 part water. The resultingmixture was then mixed to a uniform consistency. The mixed investmentwas then vibrated into the investment ring and around the wax model. Themold was allowed to dry and harden overnight. The investment ring wasthen placed in a burn out furnace at room temperature and thetemperature raised to 600° C. where upon the wax model was burnt out ofthe investment material.

The crucibles as used in these examples were prepared by slip casting.In this process a female plaster of paris mold was prepared by mixing1247.4 grams of plaster of paris with 946 ml of water to a uniformconsistency. The resulting mold was allowed to harden for 36 hours. Aslurry of a particulate crucible formulation mixture, as is identifiedin the examples below was then placed in the preformed plaster of parismold. The green crucible was removed from the mold and fired in afurnace for 15 minutes at 1100° C. to sinter the crucible to a hardenedmore durable form.

The slurry used to form the crucible was formed by mixing 1 pound ofparticulate material with 160 ml water.

Because of the hyorasiopic nature of the plaster of paris mold theparticulate crucible formulation slurry coagulates in the plaster ofparis mold. When the desired crucible wall thickness was achieved theremainder of the slurry was poured out of the mold resulting in a greencrucible structure which was allowed to dry.

In the listed examples and in this application, the coefficient ofthermal expansion (C.T.E.) was measured from room temperature to 250° C.and is reported in units of ×10⁻⁷ /°C.

The translucency of the resulting dental restoration was measured byvisual inspection given a value of 0 to 5 wherein value of 0 was deemedto be perfectly clear and 5 was deemed to be opaque.

In the below listed Examples for purposes of injecting the molten glassand glass ceramic material into the mold a pressure of 30 P.S.I wasutilized, with the exception of Examples 26, and 27 wherein a pressureof about 50 P.S.I. was utilized.

The referenced heat treating sequence for all Examples except Examples26, and 27 is in accordance with Table IV above.

In the below Examples the glass-ceramic test rods for measuring modulesof rupture (MOR) and thermal expansion (C.T.E) were formed along withcolor tab test samples. These test rods and color tab samples weresubjected to the heat treatment process of Table VI whereby the glasseswere crystallized in situ to glass-ceramics. The test rod samples were0.120"×1.25". The Examples also record the visual appearance of eachglass-ceramic and values of various properties exhibited by theglass-ceramic, such as, linear coefficient of thermal expansion(C.T.E.), reported in terms of ×10 -7/°C., modules of rupture (MOR),cited in terms of K.S.I. (thousands of pounds per square inch) asdetermined in accordance with measurement techniques conventional in theart. K.S.I. may be conversted to its metric equivalent MPa by dividingK.S.I. by 0.145.

The components used in these Examples are as follows:

Thermovest and Therovest Liquid as sold by Kerr Manufacturing Co.Romulus, Mich. 48174. 3I Fused Silica as sold by Harbison WalkerRefactories division of Indresco Inc., Pittsburg, Pa. 15223.

SP921 TF (borosilicate glass) as sold by Specialty Glass Inc. ofOldsmar, Fla. and has the following compositions in weight percent.

                  TABLE VI                                                        ______________________________________                                                SiO.sub.2                                                                           78                                                                      B.sub.2 O.sub.3                                                                     15                                                                      Al.sub.2 O.sub.3                                                                    2.5                                                                     Na.sub.2 O                                                                          4.5                                                             ______________________________________                                    

Example 1

An attempt was made to form a Glass-ceramic dental restoration inaccordance with the following procedure. A mold was prepared inaccordance with the procedure described above.

By use of slip casting techniques, a crucible was prepared in accordancewith the procedure described above by mixing 90.8 grams of SP921TF glassin 363.2 grams of 3I fused silica with 160 ml of water. After slipcasting and drying, the crucible was sintered at a temperature of 1100°C. A glass button weighing 6 grams was then placed in the crucible andpreheated to a temperature of 650° C.

The composition of the glass-ceramic material used is in accordance withcomposition #1 of Table IV.

The preheated crucible and glass-ceramic material was then placed in anapparatus which is similar to that shown in FIG. 7 and heated to atemperature of 1400° C. for a period of 10 minutes. The ram was thenactuated, the crucible was brought into contact with the mold inaccordance with the general procedure as is illustrated in FIGS. 3through 6. The crucible cracked and hence no dental restoration wasformed.

Example 2

A Glass-ceramic dental restoration was prepared in accordance with thefollowing procedure. A mold was prepared in accordance with theprocedure described above.

By use of slip casting techniques, a crucible was prepared in accordancewith the procedure described above by mixing 136.2 grams of SP921TFglass and 317.8 grams of 3I fused silica with 160 ml of water. Afterslip casting and drying, the crucible was sintered at a temperature of1100° C. A glass button weighing 6 grams was then placed in the crucibleand preheated to a temperature of 650° C.

The composition of the glass-ceramic material used is in accordance withcomposition #1 of Table IV.

The preheated crucible and glass-ceramic material was then placed in anapparatus which is similar to that shown in FIG. 7 and heated to atemperature of 1400° C. for a period of 10 minutes. The ram was thenactuated, the crucible was brought into contact with the mold inaccordance with the general procedure as is illustrated in FIGS. 3through 6.

The dental restoration was then removed from the investment material cutapart from the sprue and heat treated.

The resulting dental restoration had excellent definition and a M.O.R.of 41 K.S.I., a C.T.E. of 148, a translucency of 3.5 and a softeningtemperature of 975° C.

During the forming process, the crucible retained its structuralintegrity and formed an effective seal with the mold. Further, duringthe heat treating process, the finished dental restoration retained itsstructural integrity and did not slump or deform during heat treating.

Additional tests were conducted wherein it was determined that thecrucible of this Example deformed and sealed well at 1375° and 1425° C.

Example 3

A mold was prepared in accordance with the procedure described above.

By use of slip casting techniques, a crucible was prepared in accordancewith the procedure described above by mixing 181.6 grams of SP921TFglass and 272.4 grams of 3I fused silica with 160 ml of water. Afterslip casting and drying, the crucible was sintered at a temperature of1100° C. A glass button weighing 6 grams was then placed in the crucibleand preheated to a temperature of 650° C.

The preheated crucible without glass-ceramic material was then placed inan apparatus which is similar to that shown in FIG. 7 and heated to atemperature of 1400° C. for a period of 10 minutes.

During the heating process, the crucible lost its structural integrityand was not capable of effecting a seal with a mold. Therefore, nomolding process was carried out.

Example 4

A mold was prepared in accordance with the procedure described above.

By use of slip casting techniques, a crucible was prepared in accordancewith the procedure described above by mixing 227 grams of SP921TF glassand 227 grams of 3I fused silica with 160 ml of water. After slipcasting and drying, the crucible was sintered at a temperature of 1100°C. A glass button weighing 6 grams was then placed in the crucible andpreheated to a temperature of 650° C.

The preheated crucible and glass-ceramic material was then placed in anapparatus which is similar to that shown in FIG. 7 and heated to atemperature of 1400° C. for a period of 10 minutes.

During the heating process, the crucible melted and hence was notcapable of forming an effective seal with the mold. Therefore, nomolding process was carried out.

Example 5

Glass-ceramic dental restoration was prepared in accordance with thefollowing procedure. A mold was prepared in accordance with theprocedure described above.

By use of slip casting techniques, a crucible was prepared in accordancewith the procedure described above by mixing 118 grams of SP921TF glassand 336 grams of 3I fused silica with 160 ml of water. After slipcasting and drying, the crucible was sintered at a temperature of 1100°C. A glass button weighing 6 grams was then placed in the crucible andpreheated to a temperature of 650° C.

The composition of the glass-ceramic material used is in accordance withcomposition #1 of Table IV.

The preheated crucible and glass-ceramic material was then placed in anapparatus which is similar to that shown in FIG. 7 and heated to atemperature of 1400° C. for a period of 10 minutes. The ram was thenactuated, the crucible was brought into contact with the mold inaccordance with the general procedure as is illustrated in FIGS. 3through 6.

The dental restoration was then removed from the investment material cutapart from the sprue and heat treated.

The resulting dental restoration had excellent definition and physicalproperties as are reported with Example 2.

During the forming process, the crucible retained its structuralintegrity and formed an effective seal with the mold. Further, duringthe heat treating process, the finished dental restoration retained itsstructural integrity and did not slump or deform. Further tests wereconducted on crucibles having the composition as set forth above whereinit was determined that the crucible cracked and hence was not functionalat 1375° C. An additional test demonstrated that the crucible of thisexample deformed and sealed at 1425° C.

Example 6

A Glass-ceramic dental restoration was prepared in accordance with thefollowing procedure. A mold was prepared in accordance with theprocedure described above.

By use of slip casting techniques, a crucible was prepared in accordancewith the procedure described above by mixing 127.1 grams of SP921TFglass and 336.9 grams of 3I fused silica with 160 ml of water. Afterslip casting and drying, the crucible was sintered at a temperature of1100° C. A glass button weighing 6 grams was then placed in the crucibleand preheated to a temperature of 650° C.

The composition of the glass-ceramic material used is in accordance withcomposition #1 of Table IV.

The preheated crucible and glass-ceramic material was then placed in anapparatus which is similar to that shown in FIG. 7 and heated to atemperature of 1400° C. for a period of 10 minutes. The ram was thenactuated, the crucible was brought into contact with the mold inaccordance with the general procedure as is illustrated in FIGS. 3through 6.

The dental restoration was then removed from the investment material cutapart from the sprue and heat treated.

The resulting dental restoration had excellent definition and physicalproperties as are in accordance with Example 2.

During the forming process, the crucible retained its structuralintegrity and formed an effective seal for the mold. Further, during theheat treating process, the dental restoration retained its structuralintegrity and did not slump or deform. Additional tests were conductedon the crucible of this example wherein it was determined that thecrucible would deform and seal at both 1375° and 1425° C.

Example 7

A Glass-ceramic dental restoration was prepared in accordance with thefollowing procedure. A mold was prepared in accordance with theprocedure described above.

By use of slip casting techniques, a crucible was prepared in accordancewith the procedure described above by mixing 145.3 grams of SP921TFglass and 308.7 grams of 3I fused silica with 160 ml of water. Afterslip casting and drying, the crucible was sintered at a temperature of1100° C. A glass button weighing 6 grams was then placed in the crucibleand preheated to a temperature of 650° C.

The composition of the glass-ceramic material used is in accordance withcomposition #1 of Table IV.

The preheated crucible and glass-ceramic material was then placed in anapparatus which is similar to that shown in FIG. 7 and heated to atemperature of 1400° C. for a period of 10 minutes. The ram was thenactuated, the crucible was brought into contact with the mold inaccordance with the general procedure as is illustrated in FIGS. 3through 6.

The dental restoration was then removed from the investment material cutapart from the sprue and heat treated.

The resulting dental restoration had excellent definition and physicalproperties as are reported in accordance with example 2.

During the forming process, the crucible retained its structuralintegrity and formed an effective seal with the mold. Further, duringthe heat treating process, the dental restoration retained itsstructural integrity and did not slump or deform. Additional tests wereconducted on the crucible of this Example wherein it was determined thatthe crucible functioned at 1375° C. However at 1425° C. the crucibleslumped and hence could not be used in the process of this invention.

Example 8

A Glass-ceramic dental restoration was prepared in accordance with thefollowing procedure. A mold was prepared in accordance with theprocedure described above.

By use of slip casting techniques, a crucible was prepared in accordancewith the procedure and description described above in connection withExample 2. A glass button weighing 6 grams was then placed in thecrucible and preheated to a temperature of 650° C.

The composition of the glass-ceramic material used is in accordance withcomposition #2 of Table IV.

The preheated crucible and glass-ceramic material was then placed in anapparatus which is similar to that shown in FIG. 7 and heated to atemperature of 1400° C. for a period of 10 minutes. The ram was thenactuated, the crucible was brought into contact with the mold inaccordance with the general procedure as is illustrated in FIGS. 3through 6.

The dental restoration was then removed from the investment material cutapart from the sprue and heated treated.

The resulting test samples and dental restoration had excellentdefinition and a M.O.R. of 46.7 K.S.I., a C.T.E. of 138 a translucencyof 2.75 and a softening temperature of 975° C.

During the forming process, the crucible retained its structuralintegrity and formed an effective seal with the mold. Further, duringthe heat treating process, the finished dental restoration retained itsstructural integrity and did not slump or deform during heat treating.

Example 9

A Glass-ceramic dental restoration was prepared in accordance with thefollowing procedure. A mold was prepared in accordance with theprocedure described above.

By use of slip casting techniques, a crucible was prepared in accordancewith the procedure and description described above in connection withExample 2. A glass button weighing 6 grams was then placed in thecrucible and preheated to a temperature of 650° C.

The composition of the glass-ceramic material used is in accordance withcomposition #3 of Table IV.

The preheated crucible and glass-ceramic material was then placed in anapparatus which is similar to that shown in FIG. 7 and heated to atemperature of 1400° C. for a period of 10 minutes. The ram was thenactuated, the crucible was brought into contact with the mold inaccordance with the general procedure as is illustrated in FIGS. 3through 6.

The dental restoration was then removed from the investment material cutapart from the sprue and heated treated.

The resulting test samples and dental restoration had excellentdefinition and a M.O.R. of 43 K.S.I., a C.T.E. of 141 a translucency of3.0 and a softening temperature of 975° C.

During the forming process, the crucible retained its structuralintegrity and formed an effective seal with the mold. Further, duringthe heat treating process, the finished dental restoration retained itsstructural integrity and did not slump or deform during heat treating.

Example 10

A Glass-ceramic dental restoration was prepared in accordance with thefollowing procedure. A mold was prepared in accordance with theprocedure described above.

By use of slip casting techniques, a crucible was prepared in accordancewith the procedure and description described above in connection withExample 2. A glass button weighing 6 grams was then placed in thecrucible and preheated to a temperature of 650° C.

The composition of the glass-ceramic material used is in accordance withcomposition #4 of Table IV.

The preheated crucible and glass-ceramic material was then placed in anapparatus which is similar to that shown in FIG. 7 and heated to atemperature of 1400° C. for a period of 10 minutes. The ram was thenactuated, the crucible was brought into contact with the mold inaccordance with the general procedure as is illustrated in FIGS. 3through 6.

The dental restoration was then removed from the investment material cutapart from the sprue and heated treated.

The resulting test samples and dental restoration had excellentdefinition and a M.O.R. of 48 K.S.I., a C.T.E. of 133 a translucency of2.5 and a softening temperature of 975° C.

During the forming process, the crucible retained its structuralintegrity and formed an effective seal with the mold. Further, duringthe heat treating process, the finished dental restoration retained itsstructural integrity and did not slump or deform during heat treating.

Example 11

A Glass-ceramic dental restoration was prepared in accordance with thefollowing procedure. A mold was prepared in accordance with theprocedure described above.

By use of slip casting techniques, a crucible was prepared in accordancewith the procedure and composition described above in connection withExample 2. A glass button weighing 6 grams was then placed in thecrucible and preheated to a temperature of 650° C.

The composition of the glass-ceramic material used is in accordance withcomposition #5 of Table IV.

The preheated crucible and glass-ceramic material was then placed in anapparatus which is similar to that shown in FIG. 7 and heated to atemperature of 1400° C. for a period of 10 minutes. The ram was thenactuated, the crucible was brought into contact with the mold inaccordance with the general procedure as is illustrated in FIGS. 3through 6.

The dental restoration was then heat treated.

The resulting test samples and dental restoration had excellentdefinition and a M.O.R. of 42 K.S.I., a C.T.E. of 140 a translucency of2.5 and a softening temperature of 975° C.

During the forming process, the crucible retained its structuralintegrity and formed an effective seal with the mold. Further, duringthe heat treating process, the finished dental restoration retained itsstructural integrity and did not slump or deform during heat treating.

Example 12

A Glass-ceramic dental restoration was prepared in accordance with thefollowing procedure. A mold was prepared in accordance with theprocedure described above.

By use of slip casting techniques, a crucible was prepared in accordancewith the procedure and composition described above in connection withExample 6. A glass button weighing 6 grams was then placed in thecrucible and preheated to a temperature of 650° C.

The composition of the glass-ceramic material used is in accordance withcomposition #6 of Table IV.

The preheated crucible and glass-ceramic material was then placed in anapparatus which is similar to that shown in FIG. 7 and heated to atemperature of 1400° C. for a period of 10 minutes. The ram was thenactuated, the crucible was brought into contact with the mold inaccordance with the general procedure as is illustrated in FIGS. 3through 6.

The dental restoration was then heat treated.

The resulting test samples and dental restoration had excellentdefinition and a M.O.R. of 41.5 K.S.I., a C.T.E. of 162 a translucencyof 4 and a softening temperature of 950° C.

During the forming process, the crucible retained its structuralintegrity and formed an effective seal with the mold. Further, duringthe heat treating process, the finished dental restoration retained itsstructural integrity and did not slump or deform during heat treating.

Example 13

A Glass-ceramic dental restoration was prepared in accordance with thefollowing procedure. A mold was prepared in accordance with theprocedure described above.

By use of slip casting techniques, a crucible was prepared in accordancewith the procedure and composition described above in connection withExample 6. A glass button weighing 6 grams was then placed in thecrucible and preheated to a temperature of 650° C.

The composition of the glass-ceramic material is in accordance with acomposition #7 of Table IV.

The preheated crucible and glass-ceramic material was then placed in anapparatus which is similar to that shown in FIG. 7 and heated to atemperature of 1400° C. for a period of 10 minutes. The ram was thenactuated, the crucible was brought into contact with the mold inaccordance with the general procedure as is illustrated in FIGS. 3through 6.

The dental restoration was then removed from the investment material cutapart from the sprue and heated treated.

The resulting test samples and dental restoration had excellentdefinition and a M.O.R. of 53.5 K.S.I., a C.T.E. of 136 a translucencyof 4.0 and a softening temperature of 950° C.

During the forming process, the crucible retained its structuralintegrity and formed an effective seal with the mold. Further, duringthe heat treating process, the finished dental restoration retained itsstructural integrity and did not slump or deform during heat treating.

Example 14

A Glass-ceramic dental restoration was prepared in accordance with thefollowing procedure. A mold was prepared in accordance with theprocedure described above.

By use of slip casting techniques, a crucible was prepared in accordancewith the procedure and composition described above in connection withExample 2. A glass button weighing 6 grams was then placed in thecrucible and preheated to a temperature of 650° C.

The glass-ceramic material used was Di-Cor as sold by the DensplyCorporation and as is described above. Di-Cor is thought to beflouro-mica glass-ceramic.

The preheated crucible and glass-ceramic material was then placed in anapparatus which is similar to that shown in FIG. 7 and heated to atemperature of 1400° C. for a period of 10 minutes. The ram was thenactuated, the crucible was brought into contact with the mold inaccordance with the general procedure as is illustrated in FIGS. 3through 6.

The dental restoration was then heat treated in the investment.

While the glass-ceramic properly filled the mold the resulting dentalrestortion cracked as a result of shrinkage during the heat treatingprocess. This cracking is thought to result from the fact that theforming investment was not suitable for use in the heat treatingsequence.

Example 15

A Glass-ceramic dental restoration was prepared in accordance with thefollowing procedure. A mold was prepared in accordance with theprocedure described above.

By use of slip casting techniques, a crucible was prepared in accordancewith the procedure and composition described above in connection withExample 2. A glass button weighing 6 grams was then placed in thecrucible and preheated to a temperature of 650° C.

The composition of the glass used in weight percent was;

                  TABLE VII                                                       ______________________________________                                                SiO.sub.2                                                                           50.2                                                                    B.sub.2 O.sub.3                                                                     8.6                                                                     AlF.sub.3                                                                           .7                                                                      Al.sub.2 O.sub.3                                                                    16.0                                                                    BaO   4.75                                                                    ZnO   19.75                                                           ______________________________________                                    

The preheated crucible and glass-ceramic material was then placed in anapparatus which is similar to that shown in FIG. 7 and heated to atemperature of 1400° C. for a period of 10 minutes. The ram was thenactuated, the crucible was brought into contact with the mold inaccordance with the general procedure as is illustrated in FIGS. 3through 6.

A satisfactory dental restoration resulted which was then removed fromthe investment material cut apart from the sprue.

The resulting test samples and dental restoration had excellentdefinition and a M.O.R. of 4 K.S.I., a C.T.E. of 56 a translucency of 0.

During the forming process, the crucible retained its structuralintegrity and formed an effective seal with the mold. Because thematerial used was a glass the resulting dental restoration was not heattreated.

Example 16

Glass-ceramic dental composition was prepared and heat treated inaccordance with this invention. The composition of the glass-ceramicmaterial is in accordance with the composition No. 8 of Table IV. Aftermelting, test samples were prepared in accordance with the proceduredescribed above. The resulting test samples had a M.O.R. of 30 K.S.I., aC.T.E. of 157, a translucency of 40 and a softening temperature of 925°C.

The test samples cracked during heat treating therefore the compositionwas deemed to be unsuitable as a material for use in preparation ofdental restorations, accordingly, further tests were not carried out anda dental restoration was not formed.

Example 17

A Glass-ceramic dental composition was prepared and heat treated inaccordance with this invention. The composition of the glass-ceramicmaterial is in accordance with the composition No. 9 of Table IV. Aftermelting, test samples were prepared in accordance with the proceduredescribed above. The resulting test samples had a M.O.R. of 24 K.S.I., aC.T.E. of 145, and a softening temperature of 975° C.

Because the test samples had a M.O.R. of only 24 and the glass-ceramicwas hard to melt and form the composition was deemed to be unsuitable asa material for use in preparation of dental restorations, accordingly,further tests were not carried out and a dental restoration was notformed.

Example 18

A Glass-ceramic dental composition was prepared and heat treated inaccordance with this invention. The composition of the glass-ceramicmaterial is in accordance with the composition No. 10 of Table IV. Afterpreparation, test samples were prepared in accordance with the proceduredescribed above. The resulting test samples had a M.O.R. of 41.4 K.S.I.,a C.T.E. of 129, a translucency of 2.5 and a softening temperature of975° C.

Because the test samples had a C.T.E. of less than 130 the compositionmay not be unsuitable as a material for use in preparation of dentalrestorations, accordingly, further tests were not carried out and adental restoration was not formed.

Example 19

A Glass-ceramic dental composition was prepared and heat treated inaccordance with this invention. The composition of the glass-ceramicmaterial is in accordance with the composition No. 11 of Table IV. Afterpreparation, test samples were prepared in accordance with the proceduredescribed above. The resulting test samples had a M.O.R. of 35 K.S.I., aC.T.E. of 80, a translucency of 3.5 and a softening temperature of 975°C.

Because the test samples had a C.T.E. of 80 the composition was deemedto be unsuitable as a material for use in preparation of dentalrestorations, accordingly, further tests were not carried out and adental restoration was not formed.

Example 20

A Glass-ceramic dental composition was prepared and heat treated inaccordance with this invention. The composition of the glass-ceramicmaterial is in accordance with the composition No. 12 of Table IV Afterpreparation, test samples were prepared in accordance with the proceduredescribed above. The resulting test samples had a M.O.R. of 31 K.S.I., aC.T.E. of 127, and a translucency of 2.5.

Because the test samples had a C.T.E. of 127 therefore the compositionmay not be unsuitable as a material for use in preparation of dentalrestorations, accordingly, further tests were not carried out and adental restoration was not formed.

Example 21

A Glass-ceramic dental composition was prepared and heat treated inaccordance with this invention. The composition of the glass-ceramicmaterial is in accordance with the composition No. 13 of Table IV. Afterpreparation, test samples were prepared in accordance with the proceduredescribed above. The resulting test samples had a M.O.R. of 32 K.S.I., aC.T.E. of 256, and a translucency of 5.

Because the test samples had a C.T.E. of 256 the composition was deemedto be unsuitable as a material for use in preparation of dentalrestorations, accordingly, further tests were not carried out and adental restoration was not formed.

Example 22

Glass-ceramic dental composition was prepared and heat treated inaccordance with this invention. The composition of the glass-ceramicmaterial is in accordance with the composition No. 14 of Table IV. Afterpreparation, test samples were prepared in accordance with the proceduredescribed above. The resulting test samples had a M.O.R. of 13 K.S.I., aC.T.E. of 126, and a translucency of 4.5.

Because the test samples had a low C.T.E. and a low M.O.R. thecomposition was deemed to be unsuitable as a material for use inpreparation of dental restorations, accordingly, further tests were notcarried out and a dental restoration was not formed.

Example 23

A Glass-ceramic dental composition was prepared and elevated inaccordance with this invention. The composition of the glass-ceramicmaterial is in accordance with the composition No. 15 of Table IV. Afterpreparation, test samples were prepared in accordance with the proceduredescribed above. The resulting test samples had a translucency of 5.0.

Because the test samples turned opaque during heat treating thereforethe composition was deemed to be unsuitable as a material for use inpreparation of dental restorations, accordingly, further tests were notcarried out and a dental restoration was not formed.

Example 24

A Glass-ceramic dental restoration was prepared in accordance with thefollowing procedure. A mold was prepared in accordance with theprocedure described above.

By use of slip casting techniques, a crucible was prepared in accordancewith the procedure and composition described above in connection withExample 6. A glass button weighing 6 grams was then placed in thecrucible and preheated to a temperature of 650° C.

The composition of the glass-ceramic material used is in accordance withcomposition #16 of Table IV.

The preheated crucible and glass-ceramic material was then placed in anapparatus which is similar to that shown in FIG. 7 and heated to atemperature of 1425° C. for a period of 10 minutes. The ram was thenactuated, the crucible was brought into contact with the mold inaccordance with the general procedure as is illustrated in FIGS. 3through 6.

The dental restoration was then removed from the investment material cutapart from the sprue and heat treated.

The resulting test samples and dental restoration had excellentdefinition and a M.O.R. of 35 K.S.I., a C.T.E. of 148 translucency of3.5 and a softening temperature of 950° C.

During the forming process, the crucible retained its structuralintegrity and formed an effective seal with the mold. Further, duringthe heat treating process, the finished dental restoration retained itsstructural integrity and did not slump or deform during heat treating.

The investment material utilized was Whipmix GTJM 3-23-94; As describedherein above. The investment material had an expansion rate of about 3%.As a result of this expansion rate the resulting dental restoration hadexcellent fit.

Example 25

Glass-ceramic dental restoration was prepared in accordance with thefollowing procedure. A mold was prepared in accordance with theprocedure described above.

By use of slip casting techniques, a crucible was prepared in accordancewith the procedure and composition described above in connection withExample 6. A glass button weighing 6 grams was then placed in thecrucible and preheated to a temperature of 650° C.

The composition of the glass-ceramic material used is in accordance withcomposition #17 of Table IV.

The preheated crucible and glass-ceramic material was then placed in anapparatus which is similar to that shown in FIG. 7 and heated to atemperature of 1425° C. for a period of 10 minutes. The ram was thenactuated, the crucible was brought into contact with the mold inaccordance with the general procedure as is illustrated in FIGS. 3through 6.

The dental restoration was then heat treated in the investment material.

The resulting test samples and dental restoration had excellentdefinition and a M.O.R. of 40 K.S.I., a C.T.E. of 138 a translucency of3.5 and a softening temperature of 950° C.

During the forming process, the crucible retained its structuralintegrity and formed an effective seal with the mold. Further, duringthe heat treating process, the finished dental restoration retained itsstructural integrity and did not slump or deform during heat treating.

The investment material utilized was Thermovest and after heat treatingwas removed and the resulting dental restortion had excellent fit.

Example 26

A glass-ceramic dental restoration was prepared in accordance with thefollowing procedure. A mold was prepared in accordance with theprocedure described above.

By use of slip casting techniques, a crucible was prepared in accordancewith the procedure and composition described above in connection withExample 6. A glass button weighing 6 grams was then placed in thecrucible.

The composition of the glass-ceramic material used is in accordance withcomposition 18 of Table IV.

The crucible and glass-ceramic material was then placed in an apparatuswhich is similar to that shown in FIGS. 7a and 7b and heated to atemperature of 1425° C. for a period of 5 minutes. The ram was thenactuated, the crucible was brought into contact with the mold inaccordance with the general procedure as is illustrated in FIGS. 3through 6.

The dental restoration was then removed from the investment material cutapart from the sprue and heat treated.

The resulting test samples and dental restoration had excellentdefinition and a M.O.R. of 47 K.S.I., a translucency of 4.0 and asoftening temperature of 950° C.

During the forming process, the crucible retained its structuralintegrity and formed an effective seal with the mold. Further, duringthe heat treating process, the finished dental restoration retained itsstructural integrity and did not slump or deform during heat treating.

The investment material utilized was Whipmix GTJM3-23-94; As describedherein above. The investment material had an expansion rate of about 3%.As a result of this expansion rate the resulting dental restoration hadexcellent fit.

Example 27

A Glass-ceramic dental restoration was prepared in accordance with thefollowing procedure. A mold was prepared in accordance with theprocedure described above.

By use of slip casting techniques, a crucible was prepared in accordancewith the procedure and composition described above in connection withExample 6. A glass button weighing 6 grams was then placed in thecrucible and not preheated.

The composition of the glass-ceramic material used is in accordance withcomposition 19 of Table IV.

The crucible and glass-ceramic material was then placed in an apparatuswhich is similar to that shown in FIGS. 7a and 7b and heated to atemperature of 1425° C. for a period of 5 minutes. The ram was thenactuated, the crucible was brought into contact with the mold inaccordance with the general procedure as is illustrated in FIGS. 3through 6.

The dental restoration was then removed from the investment material cutapart from the sprue and heat treated.

The resulting test samples and dental restoration had excellentdefinition and a M.O.R. of 52 K.S.I., a translucency of 3.5 and asoftening temperature of 950° C.

During the forming process, the crucible retained its structuralintegrity and formed an effective seal with the mold. Further, duringthe heat treating process, the finished dental restoration retained itsstructural integrity and did not slump or deform during heat treating.

The investment material utilized was Whipmix GTJM3-23-94; As describedherein above. The investment material had a total expansion rate ofabout 3%. As a result of this expansion rate the resulting dentalrestoration had excellent fit.

Examples 26 and 27 represent the preferred process and glass ceramiccompositions in accordance with this invention. As is mentioned theresulting dental restorations of these Examples were heat treated theheat treating procedure used for Examples 26 and 27 is per Table VIII.

                  TABLE VIII                                                      ______________________________________                                        Heat Dental Restoration to                                                                       450° C. at furnace rate                             Ramp or soak at    450-550° C. for 6 hours                             Ramp at            550-850° C. for 2 hours                             Hold at            850° C. for 45 minutes                              Ramp at            850-900° C. at furnace rate                         Soak at            900° C. for 15 minutes                              Cool to            Room Temperature                                           ______________________________________                                    

After heat treating the dental restorations of Examples 26 and 27 werefurther finished by altering the shape and shade with a high fusingporcelain sold under the trademark Ceramco II and a low fusing porcelainsold under the trademark Final Touch. Both of the high and low fusingporcelains fired and adhered well. Likewise, both porcelains had thermalexpansions which were compatible with the glass-ceramics from which thedental restorations were formed.

The Ceramco II and Final Touch porcelains as used herein aremanufactured and sold by Ceramco, Inc. of six Terri Lane, Burlington,N.J. 08016.

Relative to the dental restorations as were produced in accordance withExamples 26 and 27 above it should be noted that these restorations wereexceptionally strong in that they had M.O.R. ratings of about 50 K.S.I.

It should be noted that the M.O.R. ratings of Examples 26 and 27 do notcorrelate with the M.O.R. ratings as are specified relative to the otherexamples in that a different test protocol was used for mearusing theM.O.R. of Examples 26 and 27. The M.O.R. for Examples 26 and 27 weretested on a Lloyd Instrument type No.TG 18 as manufactured by JohnChatilion & Sons Inc. of Greensboro, N.C. These measurements were madein accordance with I.S.0 test No. 6872 using cylindrical bars of 0.125"diameter with a 1" span, 3 point bending with a crosshead speed of 1m.m. per minute.

In contrast the M.O.R. measurements of the other Examples were made on apiece of equipment which was manufactured by the applicant. This pieceof equipment has characteristics which are similar to those of the abovedescribed Lloyd instrument type No. TG 18 and used the same test bars.Generally it could be said that the M.O.R. rating of those Examplesother than Examples 26 and 27 appear to be low.

For a corelation between the M.O.R. test protocol of Examples 26 and 27and the test protocol of the other Examples Table IX should be referredto

                  TABLE IX                                                        ______________________________________                                                   Reported M.O.R.                                                               As per test used                                                                           M.O.R. as per. I.S.O.                                 Example No.                                                                              for Examples 1-25                                                                          Test No. 6872                                         ______________________________________                                        26         42           47                                                    27         45           52                                                    ______________________________________                                    

Example 28

A glass-ceramic dental restoration was prepared in accordance with thefollowing procedure. A mold was prepared in accordance with theprocedure described above.

By use of slip casting techniques, a crucible was prepared in accordancewith the procedure and composition described above in connection withExample 6. A glass button weighing 6 grams was then placed in thecrucible and preheated to a temperature of 650° C.

The composition of the glass-ceramic material used is in accordance withcomposition 10 of Table IV.

The preheated crucible and glass-ceramic material was then placed in anapparatus which is similar to that shown in FIG. 7 and heated to atemperature of 1425° C. for a period of 10 minutes. The ram was thenactuated, the crucible was brought into contact with the mold inaccordance with the general procedure as is illustrated in FIGS. 3through 6.

The dental restoration was then heat treated.

The resulting test samples and dental restoration had excellentdefinition and a C.T.E. of 111 a translucency of 3.5 and a softeningtemperature of 850° C.

During the forming process, the crucible retained its structuralintegrity and formed an effective seal with the mold. Further, duringthe heat treating process, the finished dental restoration retained itsstructural integrity and did not slump or deform during heat treating.

It should be understood that the invention is not limited to theembodiment shown and described in FIGS. 1-10 and examples 1 to 28 sincethe process and composition parameters can be varied and theconfiguration of the apparatus can be altered without departing from thescope of the invention.

The above description and drawings are illustrative only sincemodifications could be made without departing from the presentinvention, the scope of which is to be limited only by the followingclaims.

What is claimed is:
 1. A dental restoration which is formed from aglass-ceramic material, which does not deform during heat treating,comprising the following composition (by weight percent),

    ______________________________________                                        Li.sub.2 O        8-15                                                        Al.sub.2 O.sub.3 1.5-5.0                                                      SiO.sub.2        60-85                                                        Na.sub.2 O       0-2                                                          K.sub.2 O        0-2                                                          P.sub.2 O.sub.5  1.5-5                                                        ZrO.sub.2        0-3                                                          CaO              0-1                                                          BaO + SrO + LaO   0-12                                                        Coloring Oxides  0-5                                                          ______________________________________                                    

wherein said dental restoration is further altered by applying one ormore layer(s) of a porcelain material to said dental restoration andfusing said porcelain layer(s), wherein the C.T.E. of said porcelainmaterial is slightly less than the C.T.E. of the glass ceramic material.2. A dental restoration which is formed from a glass-ceramic materialwhich does not deform during heat treating, comprising the followingcomposition (by weight percent),

    ______________________________________                                        Li.sub.2 O         10-13.5                                                    Al.sub.2 O.sub.3 2-3                                                          SiO.sub.2        70-84                                                        K.sub.2 O        0-1                                                          P.sub.2 O.sub.5  1.5-4                                                        ZrO.sub.2        0-1                                                          Ba + SrO + LaO   .5-4                                                         CaO              0-1                                                          Coloring Oxides  0-5                                                          ______________________________________                                    

wherein said dental restoration is further altered by applying one ormore layer(s) of a porcelain material to said dental restoration andfusing said porcelain layer(s), wherein the C.T.E. of said porcelainmaterial is slightly less than the C.T.E. of the glass ceramic material.3. A dental restoration of which is formed from a glass-ceramicmaterial, which does not deform during heat treating, comprising thefollowing composition (by weight percent),

    ______________________________________                                        Li.sub.2 O        9-13                                                        Al.sub.2 O.sub.3 1.5-4                                                        SiO.sub.2        65-84                                                        Na.sub.2 O       0-1                                                          K.sub.2 O        0-1                                                          P.sub.2 O.sub.5  1.5-4                                                        ZrO.sub.2        0-1                                                          BaO + SrO + LaO   0-12                                                        CaO              0-1                                                          Coloring Oxides  0-5                                                          ______________________________________                                    

wherein said dental restoration is further altered by applying one ormore layer(s) of a porcelain material to said dental restoration andfusing said layer(s) wherein the C.T.E. of said porcelain material isslightly less than the C.T.E. of the glass ceramic material.
 4. Thedental restoration which is formed from a glass-ceramic material, whichdoes not deform during heat treating, comprising the followingcomposition (by weight percent),

    ______________________________________                                               Li.sub.2 O                                                                              10.5                                                                Al.sub.2 O.sub.3                                                                        2.5                                                                 SiO.sub.2 78.5                                                                K.sub.2 O 0.5                                                                 P.sub.2 O.sub.5                                                                         2.0                                                                 ZrO.sub.2 0.5                                                                 TiO.sub.2 0.1                                                                 CeO       0.35                                                                NiO.sub.2 .02                                                                 BaO       3.0                                                                 Coloring Oxides                                                                         2.03                                                         ______________________________________                                    

wherein said dental restoration is further altered by applying one ormore layer(s) of a porcelain material to said dental restoration andfusing said layer(s), wherein the C.T.E. of said porcelain material isslightly less than the C.T.E. of the glass-ceramic material.